Engines have in the past utilized pre-chamber combustion to increase combustion efficiency and correspondingly reduce emissions. Pre-chamber combustion systems typically include an auxiliary pre-chamber above the main combustion chamber with an ignition device and fuel injector coupled to the auxiliary pre-chamber. In such systems, combustion unfolds in the following sequence; (i) a small amount of fuel is directly injected into the pre-chamber, (ii) spark is provided to the air/fuel mixture in the pre-chamber; and (iii) the hot gas jets into the main combustion chamber to ignite the charge disposed therein. Jetting the ignited gas into the main combustion chamber in this manner enables hot gas jets to penetrate deeper into the main combustion chamber, causing more evenly distributed ignition, when compared to engines that do not employ pre-chamber schemes.
One example approach shown by Attard in U.S. 2012/0103302 includes a system with an ignition assembly with a pre-chamber, a fuel injector, and a spark plug that is mounted in the cylinder head above the main combustion chamber. Attard's pre-chamber ignition system achieves fast burn in fuel-lean conditions. However, the inventors have recognized several potential drawbacks with Attard's system and other pre-chamber assemblies. For instance, residual burned gases may dwell in the pre-chamber, diluting the air/fuel mixture in subsequent combustion cycles. As a result, combustion efficiency is decreased and emissions are associatively increased. Moreover, the supplemental fuel injected into the pre-chamber may not enhance ignitability or burn rate during stoichiometric conditions. Therefore, Attard's system may only achieve efficiency gains during a limited window of engine operation. The inventors have also recognized that further problems could arise if exhaust gas recirculation (EGR) were to be employed in Attard's system or other pre-chamber combustion systems. For instance, flowing EGR into the main combustion chamber can exacerbate the problem of pre-chamber dilution which limits the applicability of pre-chamber ignitions systems for extending the tolerance of the engine to high rates of EGR (internal or external). Dilution with inert burned gas, external EGR or internal residuals, is beneficial to engine efficiency and may be limited by ignitability and by burn rate. If robust ignition can be achieved within the pre-chamber of a pre-chamber ignition system, it will accelerate the burn rate in main chamber and improve the engine dilution tolerance and engine efficiency. Attempts have been made to purge pre-chambers via air assisted injectors. However, systems employing secondary chamber air injectors have in the past required complicated controls, hardware, and mechanical assemblies to implement, thereby increasing the cost and complexity of the engine.
The inventors have recognized the aforementioned problems and facing these challenges developed a system, in one example, to address the problems. The system includes a combustion chamber formed by a cylinder head coupled to a cylinder block and a pre-chamber in fluidic communication with the combustion chamber. The system also includes a purge port coupled to the pre-chamber and structured to flow purge air into the pre-chamber, where the flow of the purge air is driven by operation a purge pump and a piston disposed within the combustion chamber. In this way, fresh air can be directed into the pre-chamber to scavenge the chamber of residual gases via purge pump operation. Purging the residual exhaust gases from the pre-chamber combustion enables combustion efficiency to be increased and emissions to be reduced. Specifically, the purging of the pre-chamber enables the burn rate to be increased and combustion stability to be improved under residual conditions, such as during EGR operation and when internal combustion chamber residuals occur.
As one example, in the system the purge pump may be a positive displacement pump including a plunger attached to an intake valve stem, the purge airflow generated by reciprocal motion of the plunger. In this way, motion of the intake valve can be used to drive a displacement pump for pre-chamber purge airflow. Consequently, the system can efficiently purge the pre-chamber without the need for additional complex and bulky purge components, controls, etc., if desired. Moreover, using intake valve movement to drive purge operation enables purge airflow to be delivered at desired time intervals (e.g., during an intake stroke), thereby avoiding mistimed purge events.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.